* {
    margin: 0;
    padding: 0;
    list-style: none;
}
html,body{
    width: 100%;
    height: 100%;
}

.mask {
    width: 100%;
    height: 100%;
    position: fixed;
    background: rgba(0, 0, 0, 0.5);
}
.cont{
    position: absolute;
    width: 100px;
    height: 100px;
    background: #fff;
    margin: auto;
    left: 0;
    right: 0;
    top:50%;
}
.tab {
    width: 100%;
    height: 500px;
    display: flex;
    border: 2px solid #000;
  }
  .left {
    width: 100px;
    height: 100%;
    margin-right: 10px;
  }
  .left li {
    border: 1px solid #ccc;
    text-align: center;
    line-height: 25px;
  }
  .right {
    flex: 1;
    height: 100%;
    overflow-y: scroll;
  }
  
  .left .on{
    background: #06f;
    color:#fff;
  }